Peripheral plasma progesterone during egg transport in the rabbit.

Peripheral plasma progesterone concentrations were measured in New Zealand rabbits every 6 hr beginning 12 hr before and continuing until 96 hr after either natural mating, hCG injection, or saline injection. The number of ovulation points in naturally mated animals (9.3 +/- 0.6, mean +/- SE) was not significantly different from that in hCG-injected animals (8.6 +/- 1.5). There was a surge in progesterone secretion following both mating and hCG injection. Plasma progesterone concentrations reached a peak prior to ovulation and then fell to basal levels at the time of ovulation. Beginning at approximately 30 hr after the ovulation-inducing stimulus, there was a progressive, significant (P less than 0.001) increase in plasma progesterone concentration, which continued for the duration of the sampling period. The initiation of the postovulatory increase in progesterone secretion corresponds temporally with the movement of eggs from the ampullary-isthmic junction into the isthmus. The progressive increase in plasma progesterone between 30 and 72 hr after the induction of ovulation corresponds with the gradual movement of eggs through the isthmus into the uterus. The data suggest that movement of eggs through the oviductal isthmus is influenced by the postovulatory secretion of progesterone.     

Conception, embryonic development and corpus luteum function in beef cattle open for two consecutive breeding seasons

High-fertility (control cows) and low-fertility (cows and heifers not pregnant after two consecutive breeding seasons — twice-open) cyclic bovine females were treated with a single injection of 1000 IU of human chrionic gonadotropin (HCG) or 100 μg of gonadotropin releasing hormone (GnRH) to enhance and/or hasten corpus luteum formation and progesterone secretion, and improve conception rate in the low-fertility females. Hormone treatments were administered to 38 parous control cows, 34 twice-open parous cows, and 27 twice-open nonparous heifers immediately after natural mating by a fertile bull. Blood samples were collected on Days 3, 6, 9, 12, and 18 after mating for determination of systemic progesterone concentrations. Pregnancy rate at necrospy approximately 33 days after mating (range 31–37) was higher in control cows (73.0%) than in twice-open cows (48.4%; P<0.05) or twice-open heifers (34.6%; P<0.01). Pregnancy rate was not affected by the HCG or GnRH treatment. The HCG treatment increased plasma progesterone concentrations in twice-open heifers but not in control or twice-open cows. Progesterone was unaffected by the GnRH treatment. Systemic progesterone concentrations were higher in control than in twice-open females but did not differ between pregnant and nonpregnant females of Days 3, 6, 9 and 12 after mating. Enhanced gonadotropin stimulation at estrus by injection of either HCG or GnRH did not increase pregnancy rate or systemic progesterone concentrations (except in HCG-treated twice-open heifers) in low- or high-fertility females. Lower pregnancy rates in twice-open females were not associated directly with the lower systemic progesterone concentrations.     

Peripheral plasma levels of progesterone, oestradiol-17 beta, oestrone, testosterone, androstenedione and chorionic gonadotrophin during pregnancy in the marmoset monkey, Callithrix jacchus.

Concentrations of LH/CG, androstenedione and testosterone rose in early pregnancy to maximum values at 6--10 weeks. Thereafter LH/CG levels declined and androstenedione and testosterone levels remained at plateau values or declined until term. Progesterone, oestradiol-17 beta and oestrone increased after ovulation and remained high throughout pregnancy. At 12 weeks, when LH/CG levels were falling, progesterone and oestradiol rose well above the luteal-phase levels which were maintained for the first 12 weeks. Progesterone declined in the 2 weeks before birth, while oestradiol and oestrone remained high. Pregnancies of an unknown stage were dated by reference to a graph of uterine diameter, measured by abdominal palpation, in animals at known times after conception. Measurement of progesterone concentrations during the conception cycle gave more accurate dating and showed that the gestation length was 144 days.     

Is the yak (Poephagus grunniens L.) really a seasonal breeder?

Yaks are considered to be seasonally polyestrous and breeding occurs from July to November. Here we show that some yaks in peak non-breeding season do exhibit cyclic luteal activity without exhibiting any behavioral signs around expected estrus. A total of eight non-lactating yaks were selected from the Yak Farm belonging to National Research Centre on Yak for various sets of experiments. The animals were maintained as per semi range system of management. They were allowed to graze during daytime and fed concentrate mixture @2 kg/animal/day as per standard farm practices of the center. Blood samples were collected on alternate days for 30 days by jugular venipuncture from the yaks during peak breeding season (July to November) and from the same yaks in non-breeding season (February to March). The plasma samples were analysed for progesterone and estradiol-17beta by RIA and EIA procedures, respectively. During breeding season, the mean plasma progesterone at estrus was basal (相似文献   

Hormonal regulation of lysosomal hydrolases in the reproductive tract of the rabbit

The total protein content and the activities of lysosomal hydrolases (arylsulphatase, alkaline and acid phosphatases, beta-glucuronidase, beta-N-acetylhexosaminidase, alpha-L-fucosidase and beta-galactosidase) in the uteri of ovariectomized rabbits treated with different concentrations of progesterone, oestradiol-17 beta and a combination of progesterone and oestradiol were determined. The enzyme activities were also measured in the reproductive organs of rabbits induced to superovulate by PMSG and hCG. In superovulated and steroid-treated rabbits, the changes in lysosomal hydrolases were more obvious in the endometrium than the myometrium. Except for the myometrial alkaline phosphatase and beta-galactosidase and the endometrial alkaline phosphatase, there were no significant changes in the solubilities of hydrolases after treatment with steroids. beta-Galactosidase levels were significantly higher in the ovariectomized rabbits treated with progesterone. An antagonistic effect of oestradiol and progesterone was observed with respect to uterine weight, protein content and enzyme activities in the ovariectomized rabbits treated simultaneously with oestradiol and progesterone.     

Mating-induced luteinizing hormone surge and ovulation in the female camel (Camelus dromedarius)

Blood samples were collected after mating from four female one-humped camels every 10 min for 9-12 h. Luteinizing hormone (LH) was quantified in plasma by radioimmunoassay using antibovine LH. Of the seven observed matings, five were followed by a release of LH, and three by an ovulation (indicated by a subsequent secretion of progesterone). LH levels at the time of mating ranged from 0.7 to 3 ng/ml. When an LH response occurred, the levels increased 1 h after mating and reached a maximum in 2-3 h (ranging from 2.9 to 19.1 ng/ml). A decrease in LH was observed starting 6 h after mating and lasting for 6 h. These results are in agreement with a coitus-induced mechanism of ovulation in the one-humped camel (Camelus dromedarius). They confirm and extend the observations reported in the bactrian camel (Camelus bactrianus).     

Endocrine profiles during doe-litter separation and the subsequent pregnancy in rabbits

This study was carried out to determine the effects of a transient doe-litter separation on plasma prolactin, LH, FSH, estradiol-17beta and progesterone concentrations before artificial insemination and during the subsequent pregnancy. Control does (n=12) had free access to nursing, whereas separated does (n=12) were kept away from their litters for 48 hours before artificial insemination. Both groups were inseminated on day 11 after parturition. Teat stimulation by suckling caused a high increase in prolactin concentrations in separated does (p < 0.0001). Basal prolactin concentrations were observed in both groups on days 8 and 18 of pregnancy. No effect of the treatment was detected on LH and FSH concentrations during the sampling period. A rise of estradiol-17beta concentrations was observed 48 hours after doe-litter separation, compared to control does and to previous values (p < 0.003). Both groups showed low progesterone concentrations before artificial insemination. Pregnant rabbits in both groups showed increased progesterone concentrations on days 8 and 18 of pregnancy. Lower estradiol-17beta concentrations were observed in control does on day 18 of pregnancy compared with separated rabbits (p < 0.003). The results suggest that a transient separation of nursing does from their litters before artificial insemination may promote high follicular steroidogenesis activity leading to increased estradiol-17beta concentrations. This hormonal change could be a result of several stimulatory actions probably triggered by the absence of suckling episodes and may affect the luteotrophic function during the subsequent pregnancy.     

Influences of retrochiasmatic surgical transection on mating and serum ovarian hormone levels in the androgenized rat

In previous studies female rats were shown to increase mating after retrochiasmatic surgical transections prior to ovariectomy and after ovariectomy with and without hormone replacement. This study was designed to determine if retrochiasmatic surgical transections (FC) or sham-FC would produce similar increased mating in androgenized rats. Four of thirty-one (13%) testosterone propionate (TP)-treated rats showed minimal mating without surgery, and 27 (87%) failed to mate. Mating occurred up to 30 days following FC, whereas temporary mating resulting from sham-FC had declined to presurgical levels by 30 days after surgery. Mating after ovariectomy was not facilitated by daily injections of 0.2μg of estradiol cypionate, but was facilitated after daily injections of 1.6 μg. TP-treated rats with FC showed more mating after 1.6 μg estradiol cypionate injections than the sham-FC and non-TP-treated controls. Serum estradiol-17β and progesterone levels at autopsy did not differ between TP-treated rats mating without surgery and those failing to mate. TP-treated rats with sham-FC surgery showed levels of estradiol-17β and progesterone similar to those of nonsurgical TP-treated rats and were combined into a single control group for comparison to the FC group. Serum levels of estradiol-17β did not differ between the control and FC group, whereas serum progesterone levels were decreased in the FC group. Serum levels of estradiol-17β and progesterone in TP-treated rats without FC were similar to baseline levels observed in this colony during the 4-day estrous cycle, but were less than peak levels observed at similar times on proestrus and diestrus Day 2, respectively. One possible effect of early androgen treatment would be to initiate a sustained inhibitory input to the mediobasal hypothalamus from the septal-preoptic area regions, thus causing deficits in mating. The lordosis responding in the androgenized rat after surgical interruption of the preoptic area-anterior hypothalamic continuum suggests that an inhibitory input was disrupted. It was further suggested that the higher mating observed in the FC group compared to the sham-FC group was not the result of higher ovarian hormone levels.     

Exposure to ovarian steroids elicits a female pattern of plasma cortisol levels in castrated male macaques.

Our recent observations (1) that there is a difference in circadian patterns of plasma cortisol levels between male and female macaques and (2) that after gonadectomy these differences in the patterns and in the levels of cortisol were reduced prompted us to investigate how 17 beta-estradiol (E2) and progesterone affect cortisol secretion in orchidectomized male rhesus macaques. Five male macaques, castrated as adults, were implanted subcutaneously with segments of silastic tubing filled with E2 and with progesterone in a manner such that the levels and the sequence of these hormones mimicked those that occur during the menstrual cycle of intact female macaques. Since previous studies had shown that the difference in cortisol patterns was due to higher levels in females during the day, these studies were conducted from 0800 to 2000 hours. Blood samples were collected in an adjacent room at 15-minute intervals. Separate trials were conducted 2 weeks after E2 was implanted and levels were 110 +/- 14 pg/ml and again 2 weeks later after progesterone was implanted and E2 levels were 59 +/- 15 pg/ml; progesterone levels averaged 4.0 +/- 0.65 ng/ml. Mean plasma concentrations of cortisol (microgram/100 ml) for the 12-hour period were three-fold higher in orchidectomized males treated with E2 (17.2) and with E2 + progesterone (18.0) than in intact males (4.9). Levels in males treated with ovarian steroids were double that (8.5 micrograms/100 ml) observed for intact females.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine profiles during doe-litter separation and the subsequent pregnancy in rabbits

This study was carried out to determine the effects of a transient doe-litter separation on plasma prolactin, LH, FSH, estradiol-17β and progesterone concentrations before artificial insemination and during the subsequent pregnancy. Control does (n=12) had free access to nursing, whereas separated does (n=12) were kept away from their litters for 48 hours before artificial insemination. Both groups were inseminated on day 11 after parturition. Teat stimulation by suckling caused a high increase in prolactin concentrations in separated does (p<0.0001). Basal prolactin concentrations were observed in both groups on days 8 and 18 of pregnancy. No effect of the treatment was detected on LH and FSH concentrations during the sampling period. A rise of estradiol-17β concentrations was observed 48 hours after doe-litter separation, compared to control does and to previous values (p<0.003). Both groups showed low progesterone concentrations before artificial insemination. Pregnant rabbits in both groups showed increased progesterone concentrations on days 8 and 18 of pregnancy. Lower estradiol-17β concentrations were observed in control does on day 18 of pregnancy compared with separated rabbits (p<0.003). The results suggest that a transient separation of nursing does from their litters before artificial insemination may promote high follicular steroidogenesis activity leading to increased estradiol-l7β concentrations. This hormonal change could be a result of several stimulatory actions probably triggered by the absence of suckling episodes and may affect the luteotrophic function during the subsequent pregnancy.     

Endocrine Changes after Mating in Pregnant and Non-Pregnant Llamas and Alpacas

Plasma concentrations of oestradiol-17ß, progesterone, 15-keto–dihydro–PGF2α and luteinizing hormone (LH) were monitored in llamas and alpacas after mating with an intact male. Concentrations of LH and PGF2α metabolite were high immediately after copulation. Ovulation occurred in 92% of the animals. The first significant increases in progesterone were recorded on day 4 after mating. In non-pregnant animals the lifespan of the corpus luteum was estimated to be 8–9 days. Luteolysis occurred in association with the release of PGF2α. In pregnant animals, a transient decrease in progesterone concentrations was observed between days 8 and 18 in both species. No significant changes in PGF2α secretion were registered during this period. Oes– tradiol–17ß concentrations were high on the day of mating, declined to low values on day 4, and started to increase again on day 8. Peak values after luteolysis in non-pregnant animals were significantly higher than those registered in pregnant ones. Furthermore, concentrations of oestradiol-17ß were elevated for a longer period in non–pregnant than in pregnant animals. The results suggest that progesterone from the corpus luteum exerts a negative influence on follicular activity in pregnant animals by reducing oes– tradiol-17ß secretion.     

Periovulatory steroid concentrations in HCG-treated rabbits.

The level of pregnenolone increased within 1 h and remained high for 4 h after an intravenous injection of HCG in conscious rabbits. Peaks for progesterone, estrogens and dehydroepiandrosterone were recorded at 2 h, and that of 20alpha-dihydroprogesterone 6 h after HCG injection. At the time of ovulation the serum concentrations of all steroids had returned to their basal levels. It seems that HCG maintained a high production of pregnenolone and promoted the synthesis of different steroids.     

Steroid levels after intramuscular injection of radioactive estradiol-17beta, estrone, progesterone and testosterone in the bovine

Eight 2 year old Hereford cows from days 8 to 12 of the estrous cycle were injected intramuscularly with 5 ml of corn oil containing 5 mg of estradiol-17beta (two cows), estrone (two cows), progesterone (two cows) or testosterone (two cows). Each cow treated with estradiol received 494 microc of estradiol-17beta-6, 7 H3 and each cow treated with estrone received 492 microc of estrone-6, 7 H3. Each cow treated with progesterone or testosterone received 400 muc of H3 compound labeled in the 7 position. Total urine was collected by urethral catheterization of the cows treated with estrogens. Blood samples for plasma and serum were collected via jugular cannulae. Blood and urine samples from estrogen-treated cows were collected hourly for the first 24 hr, at 2 hr intervals for the next 26 hr, at 4 hr intervals for the next 12 hr and at 12 hr intervals until background was reached. Blood samples were collected hourly from 1 to 8 hr after injection from progesterone or testosterone-treated cows. Plasma and serum levels of radioactive estradiol-17beta, estrone, progesterone and testosterone were similar. Blood levels of radioactivity peaked at 2 hr post-injection in cows receiving estradiol-17beta and at 3 hr in cows receiving estrone. Blood levels of labeled estradiol-17beta and estrone were nondetectable by 54 hr and 83 hr, respectively. Peak urinary excretion of radioactivity was reached at 7 hr for estradiol-17beta and at 14 hr for estrone and nondetectable levels were reached by 95 hr for estradiol-17beta and 14 hr for estrone. At these times, 15.5% of the total dose of radioactive estradiol-17beta and 17.5% of the injected estrone had been excreted in the urine. Peak blood and urinary excretion levels were reached earlier for radioactive estradiol-17beta than for estrone, and excretion of estradiol-17beta was completed more rapidly. No difference was found in plasma and serum levels for any steroid studies; thus, endogenous steroid titers in blood plasma and serum are not different in the cow.     

Daily changes in peripheral plasma progesterone concentrations in pregnant and pseudopregnant rabbits

Peripheral levels of plasma progesterone were found to be similar in pregnant New Zealand White and Dutch-belted rabbits. In early gestation progesterone concentrations rose rapidly, remained relatively constant and declined slowly during the latter third of pregnancy. Among pseudopregnant rabbits progesterone levels rose rapidly until day 11 and declined rapidly thereafter until day 19 at which time baseline values were obtained.     

Effects of indomethacin and aminoglutethimide phosphate in vivo on luteinizing-hormone-induced alterations of cyclic adenosine monophosphate, prostaglandin F, and steroid levels in preovulatory rat ovaries.

Changes in levels of cyclic adenosine monophosphate (cAMP), prostaglandin F (PGF), progesterone, testosterone, and estradiol-17beta, in preovulatory rat ovaries induced by exogenous luteinizing hormone (LH) have been measured. Ovarian cAMP reached maximal levels 15 min and 1h after LH administration by intravenous and intraperitoneal routes, respectively, and then declined to pre-LH levels by 8 h. Progesterone levels in ovaries and serum rose approximately in parallel with cAMP, but remained elevated throughout the 8-h sampling period. Ovarian testosterone increased to maximal levels 1 h after LH injection, followed by a rapid decline to below pre-LH levels. Ovarian estradiol-17beat concentrations declined steadily throughout the sampling period, reaching almost undetectable levels 8 h after LH treatment. Elevated ovarian PGF levels were observed only at the 4- and 8-h sampling times. Indomethacin treatment, 1 h before LH, prevented the LH-induced increase in ovarian PGF levels, depressed PGF values considerably in saline-injected controls but produced no significant inhibition of ovarian cAMP and progesterone levels. Aminoglutethimide phosphate depressed ovarian concentrations of all three steroids (progesterone, testosterone, and estradiol-17beta) to essentially undetectable levels, both in control and LH-injected rats, but did not alter the LH-induced changes in ovarian cAMP and PGF levels. These observations support the concept of cAMP as a mediator of the LH-induced alterations of ovarian steroidogenesis in vivo during the preovulatory period, but argue against an obligatory role of PGF in this process.     

Interrelationships between progesterone, 13,14-dihydro-15-keto PGF-2 alpha (PGFM) and LH in cyclic and early pregnant cows

Plasma progesterone and LH secretion patterns were examined in 18 mature dairy cows during the oestrous cycle and after insemination. Blood samples were collected every 15 min for 8 h per day on Days 3, 5, 6, 7, 8, 9, 10, 12, 14, 16, 17, 18, 19, 20 and 21 of the oestrous cycle, then, in the same cows, at the same times during early pregnancy. PGF-2 alpha secretion rates (as determined by plasma PGFM concentrations) were also monitored on Days 14, 16 and the day of, or equivalent to, luteal regression. Mean daily plasma progesterone concentrations were similar until Day 16 in cyclic and pregnant cows, after which values in non-pregnant animals declined. Regression analysis indicated that progesterone concentrations were best described by a quadratic expression with fitted maximum values on Day 13 in non-pregnant animals but values increased linearly over the whole period to Day 21 in pregnant cows. The frequency, amplitude and area under the curve of LH episodes showed no significant differences between cyclic and pregnant animals. In pregnant cows, the amplitude and area under the curve of progesterone episodes increased linearly between Days 8 and 21, although no such increase occurred in cyclic cows. Low-level PGFM episodes were present in cyclic and pregnant cows on Days 14 and 16 after oestrus, and high amplitude episodes occurred in non-pregnant cows during luteal regression. Pregnant cows showed a significant depression of the amplitude, but not the frequency of episodes at the expected time of luteal regression. These results confirm that the corpus luteum of pregnancy secretes an increasing amount of progesterone per se and per unit of LH until at least Day 21 after mating. They further suggest that the corpus luteum of the cyclic cow may experience small episodes of PGF-2 alpha and be subjected to initial degenerative changes by Day 14 after oestrus, some time before the onset of definitive luteolysis.     

In-vivo and in-vitro steroidogenic activity of post-ovulatory ovarian follicles of the rabbit

Pseudopregnancy was induced in rabbits by injection of 50 i.u. hCG into the lateral ear vein. Blood was collected on Days 0, 1, 2 and 6 after hCG from the lateral ear vein and, in some studies, from the ovarian vein as well. Ovaries were collected on Days 0, 1, 2 or 6 after hCG injection, and follicles (greater than 0.8 mm diam.) were obtained by microdissection. Concentrations of oestradiol-17 beta, testosterone and progesterone in blood and follicular homogenates were measured by RIA. Follicular steroidogenesis was increased significantly on Day 6 after ovulation, at the time when the corpus luteum transforms into an oestrogen-dependent tissue. The ability of developing post-ovulatory follicles to secrete steroids in vitro in response to a gonadotrophic stimulus also increased over this same time interval. Follicular oestradiol production on Days 1 and 2 of pseudopregnancy may synergize with the post-ovulatory secretion of FSH to promote further follicular growth in the pseudopregnant rabbit.     

A physiological dose of estradiol with progesterone affects striatum biogenic amines

The acute effect of estradiol and progesterone on dopamine and serotonin metabolism in rat striatum was studied. One subcutaneous injection of 17 beta-estradiol (300 ng) and progesterone (150 micrograms) into intact male rats increased plasma levels of these steroids, while testosterone, corticosterone, and estrone remained unchanged. Dehydroepiandrosterone, androstane-3 beta, 17 beta-diol and dihydrotestosterone remained undetectably low. Prolactin decreased and androstane-3 alpha, 17 beta-diol, and 17-OH progesterone increased, but less than estradiol and progesterone. Peak levels of striatal dopamine, dihydroxyphenylacetic acid, and homovanillic acid were observed 15-45 min after steroid injection with a return to control values after 45-60 min, while serotonin and 5-hydroxyindoleacetic acid levels were slightly decreased. An injection of estradiol (70 ng) with progesterone (70 micrograms) to ovariectomized female rats left plasma prolactin levels unchanged, while striatum dopamine and serotonin as well as their metabolite concentrations peaked 15-60 min after steroid injection and returned to control values after 45-75 min. To allow for a better comparison of the action of these steroids, the effect of estradiol or progesterone alone and in combination on the brain of ovariectomized rats was compared in the same experiment. A similar increase in metabolites of dopamine levels was observed after these steroids alone or in combination, while dopamine levels were increased only after progesterone alone or in combination with estradiol. An injection of estradiol or progesterone to ovariectomized rats led to peak steroid concentrations at approximately the same time in the brain and plasma. In addition, plasma and brain steroid levels were significantly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma relaxin levels in pregnant and lactating dogs

The pattern of plasma relaxin has been studied during pregnancy and following parturition in two breeds of dogs, Labrador retrievers and beagle hounds. Blood samples were collected at weekly intervals following mating and during pregnancy, parturition, and lactation. Relaxin, progesterone, and estradiol-17 beta were determined by specific double antibody radioimmunoassays. Immunoreactive relaxin (IR) was not detectable in plasma of male dogs, bitches in anestrous, or pseudopregnant bitches that had undergone an infertile mating. IR was first detectable in plasma in the third or fourth week of gestation in retrievers and beagles. IR levels rose to a peak of 4-5 ng/ml in both breeds. The peak plasma levels were reached 2-3 wk before whelping and declined significantly prior to that event. IR then persisted during lactation at a level of 0.5-2 ng/ml for 4-9 wk, but was significantly higher (p less than 0.01) at all time periods and persisted longer in labradors than in beagles. The secretion of relaxin did not parallel that of progesterone, which was highly elevated in the first samples drawn (during the first week of pregnancy), remained high through 5 or 6 wk of gestation, then slowly declined until the time of parturition, becoming undetectable during lactation. Plasma estradiol-17 beta was low after the second week of pregnancy in both breeds of dogs and became undetectable during lactation. The source of relaxin in the dog is not known currently, and its sites of secretion and role in pregnancy are currently under investigation in our laboratories. The dog is the first species in which plasma IR is detectable during lactation using antibody R6.(ABSTRACT TRUNCATED AT 250 WORDS)     

Concentrations of steroids and gonadotropins in follicular fluid from normal heifers and heifers primed for superovulation

The concentrations of six steroids and of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in follicular fluid from preovulatory and large atretic follicles of normal Holstein heifers and from preovulatory follicles of heifers treated with a hormonal regimen that induces superovulation. Follicular fluid from preovulatory follicles of normal animals obtained prior to the LH surge contained extremely high concentrations of estradiol (1.1 +/- 0.06 micrograms/ml), with estrone concentrations about 20-fold less. Androstenedione was the predominant aromatizable androgen (278 +/- 44 ng/ml; testosterone = 150 +/- 39 ng/ml). Pregnenolone (40 +/- 3 ng/ml) was consistently higher than progesterone (25 +/- 3 ng/ml). In fluid obtained at 15 and 24 h after the onset of estrus, estradiol concentrations had declined 6- and 12-fold, respectively; androgen concentrations had decreased 10- to 20-fold; and progesterone concentrations were increased, whereas pregnenolone concentrations had declined. Concentrations of LH and FSH in these follicles were similar to plasma levels of these hormones before and after the gonadotropin surges. The most striking difference between mean steroid levels in large atretic follicles (greater than 1 cm in diameter) and preovulatory follicles obtained before the LH surge was that estradiol concentrations were about 150 times lower in atretic follicles. Atretic follicles also had much lower concentrations of LH and slightly lower concentrations of FSH than preovulatory follicles. Hormone concentrations in follicles obtained at 12 h after the onset of estrus from heifers primed for superovulation were similar to those observed in normal preovulatory follicles at estrus + 15 h, except that estrogen concentrations were about 6-40 times lower and there was more variability among animals for both steroid and gonadotropin concentrations. Variability in the concentrations of reproductive hormones in fluid from heifers primed for superovulation suggests that the variations in numbers of normal embryos obtained with this treatment may be due, at least in part, to abnormal follicular steroidogenesis.